CN111330569A - A kind of atomically dispersed electrochemical catalyst of noble metal that can be scaled up in batches and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of electrochemical catalysis, and particularly relates to a noble metal atomic-level dispersed electrochemical catalyst capable of being amplified in batches and a preparation method thereof, wherein the electrochemical catalyst comprises the following steps: 1) preparing an organic framework structure material; 2) chelating an organic framework structure material with noble metal ions; 3) preparing a precursor solution of a noble metal macrocyclic organic substance containing a decomposition type pore-forming agent; 4) carrying out hydrothermal crystallization treatment on the noble metal macrocyclic organic precursor solution to obtain noble metal macrocyclic organic precursor powder; 5) and (3) integrating the further pyrolysis reduction and carbonization of the precursor powder of the noble metal macrocyclic organic matter. The catalyst has the advantages of simple preparation method, easily obtained and cheap raw materials, improved utilization rate of noble metals, auxiliary chelating of macrocyclic active sites, no separation of toxic impurity metals, and high graphitization degree, so that high stability can be maintained.

Description

A mass-scaled noble metal atomically dispersed electrochemical catalyst and the same Preparation

technical field

The invention belongs to the technical field of electrochemical catalysis, and in particular relates to an atomically dispersed noble metal catalyst and a preparation method thereof.

Background technique

Noble metal electrochemical catalysts are materials that use noble metals for electrochemical catalysis. Because noble metals are expensive and have a wide range of applications, they are mostly prepared as supported noble metal catalyst materials for use, such as Pt/C, Pd/C, IrO ₂ , RuO ₂ , Rh/C, Pt/ATO, etc., as a material that can change the chemical reaction rate but does not participate in the final product of the reaction, almost all precious metals can be used as catalysts, but the commonly used precious metal materials are mainly platinum, palladium, rhodium, Silver, ruthenium, etc., among which platinum and rhodium are the most widely used, because their d electron orbitals are not filled, the surface is easy to adsorb reactants, and the strength is moderate, which is conducive to the formation of intermediate "active compounds", and has high catalytic activity. It also has comprehensive excellent properties such as high temperature resistance, oxidation resistance and corrosion resistance, and is the most important catalyst material.

Precious metals have important applications in electrochemical catalysis. The proton exchange membrane fuel cell is a clean and efficient energy conversion device that converts the chemical energy in the fuel and oxidant into electrical energy, and has been widely used in cogeneration, stationary power stations, transportation, portable power and other fields. Due to the slow kinetics of the oxygen reduction reaction at the cathode of fuel cells, a large amount of noble metal Pt catalysts is required, resulting in high production costs. In addition, factors such as the decay of catalyst activity limit the lifetime of the PEMFC. The most direct and critical impact of catalyst on the cost and life of PEMFC is: the activity and stability of the noble metal Pt catalyst in the catalyst, and the loss of catalyst activity leads to the degradation of battery performance. Therefore, improving the utilization rate of Pt and preparing Pt-based catalysts with high activity and high stability is one of the focuses of fuel cell research.

Solid polymer water electrolysis technology is an energy utilization method that can be well combined with renewable energy. It can use surplus electrical energy to electrolyze water into hydrogen and oxygen, and convert surplus electrical energy into chemical energy for storage. This process has a large polarization overpotential and requires a large amount of noble metal Ir, Ru, and Pt-based catalysts. Anode oxygen evolution electrochemical catalysts for water electrolysis mainly use catalysts such as IrO ₂ , Ir, and PtIr to reduce electrolysis overpotential and improve catalytic activity. At the same time, due to the stable properties of Ir and IrO ₂ , they can work stably at high potential. There is still an irreplaceable role in the process of polymer water electrolysis. In commercial applications, Pt-based catalysts, such as Pt black, Pt/C, etc., are mainly used for polymer hydroelectrolysis hydrogen desorption catalysts.

Due to the special properties of metal palladium, it is very suitable for the manufacture of catalysts for hydrogenation and dehydrogenation reactions. In the acidic electrochemical system, the stability of Pd catalyst has certain problems. Therefore, it is often used to form alloys with Pt, Ir, etc. for hydrogen evolution and hydrogen oxidation catalytic reactions.

In addition, since 1974, the use of platinum, palladium and rhodium ternary precious metal catalysts, referred to as three-way catalysts, has been widely used in automobile exhaust purification, and it has quickly developed into the most used precious metal catalysts. Since the development and application of precious metal catalysts for more than 100 years (1875-1994), the development momentum has been prosperous. New varieties, new preparation methods, and new application fields are constantly emerging, and relevant basic theories are constantly being improved. However, due to the scarcity and high price of precious metal resources, people are constantly researching more effective use of precious metal catalysts, reducing the amount of precious metals and improving catalytic efficiency. The invention aims to prepare a mass-produced noble metal atom-dispersed catalyst by a method of pyrolysis reduction, so as to improve the utilization rate, stability and catalytic performance of the noble metal.

For proton exchange membranes and solid polymer water electrolysis systems, due to the wide use of solid polymer electrolyte membranes, there is a high requirement for the purity of the catalyst. The precious metal ions Pt ⁴⁺ and Ir ⁴⁺ dissolved in the catalyst are unstable metal ions in the catalyst. Fe ³⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , etc., as well as Na ⁺ , Ca ²⁺ , K ⁺ plasma mixed in the pipeline water will adsorb, replace or underpotential deposition on the membrane, and the proton conduction of the membrane will be improved. Destructive effects on energy and service life. Therefore, it is of great significance to improve the catalyst stability and reduce the presence of unstable ions in the catalyst.

SUMMARY OF THE INVENTION

The technical problem to be solved by the invention

In the electrochemical catalysis process, the Pt/C catalyst is mainly used in the Pt/C membrane fuel cell. The activity of the catalyst has a decisive influence on the cost, life and performance of the fuel cell. The catalyst cost accounts for more than 40%, therefore, the research of high activity and high stability Pt catalyst has an important influence. For the solid polymer water electrolysis system, a large number of Pt-based and Ir-based catalysts are used, which play an irreplaceable role in the high-potential electrocatalysis process. By increasing the utilization of precious metals, reducing catalyst costs has positive implications for electrocatalytic processes.

Methods for solving technical problems

In view of the above-mentioned problems, the present invention proposes an electrochemical catalyst with atomic dispersion of noble metals that can be scaled up in batches and a related preparation method, which includes the following steps: 1) preparation of organic framework structure materials; 2) organic framework structure materials Process of chelating with precious metal ions; 3) Preparation of precious metal macrocyclic organic precursor solution containing decomposing pore-forming agent; after adding pore-forming agent first, after uniform dispersion, and then co-settling. 4) the process of hydrothermal crystallization of the precious metal macrocyclic organic precursor solution to obtain the precious metal macrocyclic organic precursor powder; 5) the process of further pyrolysis reduction and carbonization integration of the precious metal macrocyclic organic precursor powder.

In one embodiment, in step 1), under the action of surfactant, macrocyclic organic molecules combine and react to form a stable organic framework structure material.

One embodiment is, wherein, in step 1), the temperature range of the macrocyclic organic molecule binding and reaction is 90～140°C, and the reaction time is 0.5h～3.5h;

The surfactant described in step 1) is an ionic surfactant, and the surfactant accounts for 3-15% of the organic material charging ratio;

Step 1) The macrocyclic organic molecules used to form the organic framework include three kinds, one is a macrocyclic organic compound I with nucleophilic and electrophilic addition functional groups; the other is a heterocyclic structure, which is prone to nucleophilic and electrophilic reactions. Macrocyclic organic compound II; the third is polyhydroxy functional group macrocyclic organic compound III. The ratio of macrocyclic organic compounds I, II and III ranges from 1 to 4:1 to 4:1, accounting for 80 to 97% of the total organic compound added. Part of the system needs to adjust the combined environment, the amount of alkali added is 0-5%, and the pH range is adjusted to 5-8. The pH regulator of the chelation system is NaOH, KOH, Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , KHCO ₃ , (NH ₄ ) ₂ CO ₃ , urea and other common alkaline materials, which promote the chelation reaction. conduct.

In one embodiment, in step 2), a dilute solution containing precious metal ions is added to the solution containing the organic framework structure material, so that the macrocyclic organic framework structure material and the precious metal ions are fully chelated.

One embodiment is, wherein, the precious metal chelation reaction temperature in step 2) is 90-140°C, and the reaction time is 0.5h-3.5h;

The precious metal dilute solution described in step 2) is one or more of the acids, bases and salts of the precious metal elements of Pt, Pd, Ir, Ru, Rh, Au and Ag; the solvent used includes H ₂ O, CH ₃ CH ₂ A mixed solution of one or more of OH, ethylene glycol, propanol, and isopropanol; the solution concentration is 0.005-0.15 mol/L.

In one embodiment, in step 3), a slow-release pH regulator is added to adjust the pH value of the system to promote the sedimentation and acquisition of the precursor; a decomposing pore-forming agent is added to obtain a precious metal macrocyclic organic precursor solution.

In one embodiment, the reaction time after pH adjustment in step 3) is 0.5h-3.5h, and the reaction temperature is 90-140°C; after the decomposable pore-forming agent is added, it is fully homogenized and stirred , the reaction temperature is 90～140℃, and the reaction time is 0.5h～3.5h;

Step 3) Adjusting the pH value in the range of 6 to 9, the pH adjusting agent includes urea, potassium citrate, ammonium carbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, sodium thiosulfate, ammonium bicarbonate, diethylenetriamine , a mixture of one or more of aniline, triethylenetetramine, ethylenediamine, 1,10-o-phenanthroline or 2,2'-bipyridine;

The decomposable pore-forming agent is easily decomposed salt and organic matter, and the pore-forming agent accounts for 20-45% of the total amount of the added material. Additives include all non-volatile surfactants, macrocyclic organics, metal precursors, pH adjusters and other raw materials.

One embodiment is, wherein, in the hydrothermal crystallization treatment in step 4), the reaction temperature of precursor growth and aging is 90-140° C., and the reaction time is 10-48 h; in step 4), the hydrothermal crystallization treatment is carried out. Then, carry out drying treatment, the temperature of the drying treatment is 60-100°C, and the time is 6-16h; the temperature of the further integrated treatment of pyrolysis reduction and carbonization described in step 5) is 600-1000°C, and the time is 0.5 ~4h. In step 5), when the precursor powder is further integrated with pyrolysis reduction and carbonization, the treated atmosphere is one or more of neutral or reducing gases; the heating rate is 1°C/min to 15°C/min; the protective gas flow Speed 80～400sccm/min.

According to a second aspect of the present invention, there is provided a catalyst prepared according to the above-described method.

According to a third aspect of the present invention, there is provided an electrochemical catalyst with atomic dispersion of noble metals that can be scaled up in batches, wherein, elemental analysis on the surface of the catalyst: carbon atomic percentage 82-91% (atomic), N accounting for 1.5-5 % (atomic); O element atomic percentage 2-6%; surface Pt accounts for 0.3-4% (atomic), Zn2p accounts for 0.5-6% (atomic); bulk precious metal loading 1-20%, metal particle size The size is 2-4 nm; the catalyst structure is mainly spherical.

The beneficial effects of the present invention

(1) The present invention proposes a preparation technology for preparing an electrochemical catalyst with an atomic-level dispersion of noble metals in an integrated structure in batches by a method of pyrolysis reduction. The catalyst prepared by the method has clean components, no harmful ions are precipitated during use, and has no toxic effect on the polymer membrane, and can be directly and practically applied in fuel cells and solid polymer water electrolysis systems. The catalyst preparation technology can also be used in the preparation of common electrochemical catalysts such as oxygen reduction, hydrogen evolution, oxygen evolution, hydrogen oxidation, alcohol oxidation, sulfur dioxide oxidation, and carbon dioxide reduction, and has wide application value. It is of great significance to reduce the cost of catalysts and reduce the use of precious metals such as Pt.

(2) The catalyst is a noble metal atomically dispersed electrochemical catalyst with dual active sites of metal element and macrocyclic chelate structure. The catalyst has high activity, high stability, adjustable noble metal loading, high specific surface area and graphitization degree, and is a graphene-like sheet material with mosaic structure.

(3) The preparation method of the catalyst is simple, the one-time preparation amount reaches the gram level and is easy to scale up, and the raw materials are readily available and cheap, and it has important application value in the field of electrochemical catalysis such as solid polymer water electrolysis and fuel cells. The catalyst mainly forms an atomically dispersed precious metal integrated catalyst, which increases the anchoring and inlaying of the precious metal, improves the bonding strength between the metal and the skeleton carrier, and increases the stability of the catalyst. It is of great significance to reduce the cost of catalysts and reduce the use of precious metals such as Pt.

(4) Electrochemical tests such as linear voltage sweep and cyclic voltammetry prove that the catalyst has high electrocatalytic activity, which is superior to commercial Pt/C catalysts. Through accelerated aging test, it is proved that the catalyst has good electrochemical stability.

In a word, the present invention proposes an integrated structure catalyst preparation technology, which realizes the atomic dispersion of noble metals, improves the utilization rate of noble metals, and the integrated framework material has auxiliary chelating macrocyclic active sites, which further improves the catalyst performance. Catalytic performance, pure catalyst components, no precipitation of toxic impurities metal, and high degree of graphitization (ID / _IG = _0.89 ~ 1.11), so it can maintain high stability, precious metals in the field of electrocatalysis such as fuel cells and water electrolysis The increased utilization, increased activity and stability, and reduced precious metal loading and cost are of great significance. The catalyst preparation method is simple, suitable for large-scale preparation and process amplification, and has important practical application value.

Further features of the present invention will become apparent from the following description of exemplary embodiments.

Description of drawings

Figures 1(a)-(c) are TEM images of the catalyst prepared in Example 1 of the present invention. (a) 100 nm; (b) 50 nm; (c) 10 nm;

FIG. 2 is the XRD pattern of the catalyst prepared in Example 1 of the present invention.

Figures 3(a)-(d) are XPS elemental analysis charts of the catalyst prepared in Example 1 of the present invention. Among them (a) XPS image of N1s, (b) XPS image of Pt4f, (c) XPS image of O1s, (d) XPS image of Zn2p

Figures 4(a)-(b) are the electrochemical performance characterization diagrams of the catalyst prepared in Example 2 of the present invention. (a) The electrochemical activity test of the catalyst prepared in N2 atmosphere; (b) the oxygen reduction activity test of the prepared catalyst.

Figures 5(a)-(b) are the electrochemical performance characterization diagrams of the catalyst prepared in Example 1 of the present invention. (a) The electrochemical activity test of the catalyst prepared in _H2 atmosphere; (b) the comparison of the oxygen reduction activity of the prepared catalyst.

Figures 6(a)-(b) are the electrochemical performance characterization diagrams of the catalyst prepared in Example 1 of the present invention. (a) The electrochemical activity comparison of the prepared catalyst and the commercial Pt/C catalyst; (b) the comparison of the oxygen reduction activity of the prepared catalyst and the commercial catalyst.

Figures 7(a)-(b) are the electrochemical performance characterization diagrams of the catalyst prepared in Example 3 of the present invention. Performance comparison of catalysts prepared in different atmospheres.

Detailed ways

One embodiment of the present disclosure will be specifically described below, but the present disclosure is not limited thereto.

A method for preparing a noble metal atomically dispersed electrochemical catalyst that can be scaled up in batches, the specific preparation steps are as follows:

1) Synthesis of macrocyclic organic skeleton structure: adding surfactant, fully dissolving and dispersing, heating up to the reaction temperature of 90-140 °C for the combination of macrocyclic organic molecules, and performing nucleophilic, electrophilic and other binding reactions, and the reaction time is 0.5h～ 3.5h, a stable organic skeleton structure was formed;

2) chelation fixation and atomic dispersion of precious metals: add precious metal dilute solution, control the reaction temperature and time, so that macrocyclic organic matter and precious metal ions are fully chelated; the precious metal chelation reaction temperature is 90-140 ℃, and the reaction time is 0.5h～3.5h;

3) pH control and pore-forming agent addition: add a slow-release pH regulator to adjust the pH value of the system, control the reaction temperature and time, and promote the sedimentation and acquisition of the precursor; add a decomposing pore-forming agent to provide support for subsequent high-temperature heat treatment, The pore-forming agent dissipates during the pyrolysis process and does not have a deleterious effect on catalyst purity; thereby obtaining a precious metal macrocyclic organic precursor solution. The reaction time after pH adjustment is 0.5h～3.5h, and the reaction temperature is 90～140°C; after the pore-forming agent is added, it is fully homogenized, and under stirring, the reaction temperature is 90～140°C, and the reaction time is 0.5h～ 3.5h;

4) Growth and aging of metal chelated organic compounds: pour the precursor into a hydrothermal kettle, control the reaction temperature and time, and carry out further growth and aging of the precursor of the precious metal macrocyclic organic compound; centrifuge and dry to obtain the precious metal macrocyclic compound Organic precursor powder; the growth and aging reaction temperature of the precursor is 90-140°C, and the reaction time is 10-48h. The drying treatment temperature is 60～100℃, and the time is 6～16h;

5) Integration of pyrolysis reduction and carbonization: further integration of pyrolysis reduction and carbonization of the precious metal macrocyclic organic precursor powder; thereby obtaining atomically dispersed high activity noble metal catalysts. The temperature of the integrated treatment of pyrolysis reduction and carbonization is 600-1000°C, the time is 0.5-4h, and the heating rate is 1-15°C/min.

Further, the surfactant is an ionic surfactant, such as sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, fatty acid soap, quaternary ammonium salt, lecithin, amino acid, betaine, lauramide It is a surfactant with both hydrophilic and lipophilic groups, which generates ions after dissolution and has emulsifying activity. The surfactant accounts for 3 to 15% of the organic material feed ratio. Part of the system needs to add alkali to adjust the combined environment, the addition amount is 0-5%, and the pH range is adjusted to 5-8. The pH regulator of the chelation system is NaOH, KOH, Na ₂ CO ₃ , NaHCO ₃ , K ₂ CO ₃ , KHCO ₃ , (NH ₄ ) ₂ CO ₃ , urea and other common alkaline materials, which promote the chelation reaction. conduct.

Further, the macrocyclic organic molecules used to form the organic framework include three kinds, firstly including tannic acid, lauric acid, tannic acid, cinnamic acid, gallic acid, salicylic acid, tartaric acid, malic acid, benzoic acid, water Aldehyde, diazobenzenesulfonic acid and other organic compounds rich in carboxyl and aldehyde groups with nucleophilic and electrophilic addition functional groups; and heterocyclic structures such as N, P, S, B, etc., which are prone to nucleophilic and electrophilic addition Reacted organics II, such as imidazole, cinchonine, methylimidazole, dimethylimidazole, imidazolyl amino acids, histidine, etc.; and polyhydroxy functional group organics III, such as ascorbic acid, glucose, xylitol, fructose, chitosan, Phenol, resorcinol, etc., are prone to elimination reaction, organic replacement, substitution reaction, and organic matter such as hydrogen bond formation. The ratio of organic matter I, II, and III ranges from 1 to 4:1 to 4:1, accounting for 80 to 97% of the total organic matter added.

Further, the precious metal dilute solution is one or more of acids, bases, salts, etc. of precious and precious metal elements such as Pt, Pd, Ir, Ru, Rh, Au, and Ag; for example, the Pt precursor includes H ₂ PtCl ₆ , K ₂ PtCl ₄ , ammonium chloroplatinate, platinum acetylacetonate, Pt(NH ₃ ) ₆ Cl ₂ , Pt(NH ₃ ) ₄ Cl ₂ , Pt(NO ₂ ) ₂ (NH ₃ ) ₂ ; the The Ir precursor includes chloroiridic acid, iridium chloride, etc.; the Pd precursor includes chloropalladic acid, potassium chloropalladate, palladium chloride, and the like. The solvent used includes one or a mixed solution of H ₂ O, CH ₃ CH ₂ OH, ethylene glycol, propanol, and isopropanol. The solution concentration is 0.005～0.15mol/L.

Further, for the pH adjustment for sustained release, the pH adjustment range is 6 to 9, and the pH adjustment agent includes urea, potassium citrate, ammonium carbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, and sodium thiosulfate. , One or more mixtures of ammonium bicarbonate, diethylenetriamine, aniline, triethylenetetramine, ethylenediamine, 1,10-o-phenanthroline or 2,2'-bipyridine . The pore-forming agent gradually decomposes and dissipates in the process of pyrolysis and reduction. It is mainly composed of easily decomposed salts and organic substances, including ZnCl ₂ , SnCl ₄ , FeCl ₃ , nickel chloride and other low-boiling point metal salts and ammonium chloride and ammonium hypochlorite. , oxalic acid, ammonium bicarbonate, ammonium carbonate, ammonium citrate and other high-temperature decomposition organics, and the pore-forming agent accounts for 20-45% of the total amount of the added material.

Further, the atmosphere for the further pyrolysis reduction and carbonization integrated treatment of the precursor powder is: methane, nitrogen, hydrogen, H ₂ /He, H ₂ /CO, H ₂ /CO ₂ , H ₂ /N ₂ , H ₂ /Ar, ammonia, NH ₃ /N ₂ , NH ₃ /Ar, carbon monoxide and other neutral or reducing atmospheres; the heating rate is 1℃/min～15℃/min; the protective gas flow rate is 80 ～400sccm/min, the reaction temperature is 600～1000℃, and the holding time is 0.5～4h, so as to obtain atomically dispersed high activity noble metal catalyst.

The preparation technology of atomically dispersed noble metal catalyst prepared by the above method is a method for preparing electrochemical catalyst which can be scaled up in batches. Dispersed precious metal catalysts greatly improve the utilization rate of precious metals; high-temperature pyrolysis and carbonization reduction promote the formation of organic frameworks to form an integrated structure catalyst with high degree of graphitization and high conductivity. A noble metal catalyst with a highly stable porous framework structure is obtained, and the activity and life of the catalyst are improved. The catalyst preparation method is simple, easy to scale up, and can realize the batch preparation of the catalyst, which has positive significance for industrial production. The catalyst preparation method has the characteristics of adjustable noble metal loading, high activity and stable structure. It has important application value in electrochemical catalysis such as oxygen.

Elemental analysis of the catalyst surface: 82-91% of carbon atoms (atomic), 1.5-5% of N (atomic); 2-6% of O element elements; 0.3-4% of surface Pt (atomic), Zn2p It accounts for 0.5-6% (atomic); the total loading of bulk precious metals is 1-20%, and the metal particle size is 2-4 nm; the catalyst structure is mainly spherical. The amount of catalyst Pt is low, and the oxygen reduction activity is comparable to that of commercial Pt/C catalysts, which is of great significance for reducing catalyst costs, reducing the use of precious metals such as Pt, and improving Pt utilization.

To achieve the above object, the specific preparation steps of the present invention include:

First, add a surfactant to fully dissolve and disperse, heat up to a reaction temperature of 90-140 °C for the combination of macrocyclic organic molecules, and carry out nucleophilic and electrophilic binding reactions. The reaction time is 0.5h to 3.5h to form a stable organic framework. structure;

Then, adding a precious metal dilute solution into the macrocyclic organic matter reaction solution, to carry out the sufficient adsorption and chelation of organic matter and metal ions, and controlling the reaction temperature and time to make the macrocyclic organic matter and precious metal ions fully react; the precious metal chelation reaction temperature is 90～140℃, and the reaction time is 0.5h～3.5h;

Then, a slow-release pH regulator is added to the reaction solution to adjust the pH value of the system, control the reaction temperature and time, and promote the sedimentation and acquisition of the precursor; then a decomposing pore-forming agent is added to provide support for the subsequent high-temperature heat treatment. The porogen will be dissipated during the pyrolysis process without detrimental effect on catalyst purity; fully reacted to obtain a precious metal macrocyclic organic precursor solution. The pH adjustment range is 6-9, the reaction time is 0.5h-3.5h, and the reaction temperature is 90-140°C; after the pore-forming agent is added, it is fully homogenized, and under stirring, the reaction temperature is 90-140°C, The reaction time is 0.5h～3.5h;

Subsequently, the precursor was poured into a hydrothermal kettle, and the reaction temperature and time were controlled to further grow and age the precursor of the noble metal macrocyclic organic compound; the precursor growth and ageing reaction temperature was 90-140°C, and the reaction Time 10 ~ 48h. Afterwards, centrifuge and dry to obtain the precious metal macrocyclic organic precursor powder; the drying treatment temperature is 60-100° C., and the time is 6-16 hours.

Finally, the noble metal macrocyclic organic precursor powder is further integrated by pyrolysis reduction and carbonization; thereby obtaining an atomically dispersed high activity noble metal catalyst. The temperature of the integrated treatment of pyrolysis reduction and carbonization is 600-1000°C, the time is 0.5-4h, and the heating rate is 1-15°C/min.

The surfactant is an ionic surfactant, such as sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, fatty acid soap, quaternary ammonium salt, lecithin, amino acid, betaine, lauramide, etc. A surfactant with a hydrophilic group and a lipophilic group, which generates ions after dissolution and has emulsifying activity. The surfactant accounts for 3 to 15% of the organic material feed ratio.

The macrocyclic organic molecules used to form the organic skeleton include three types, first including tannic acid, lauric acid, tannic acid, cinnamic acid, gallic acid, salicylic acid, tartaric acid, malic acid, benzoic acid, salicylic acid. Aldehyde, diazobenzenesulfonic acid and other organic compounds rich in carboxyl and aldehyde groups with nucleophilic and electrophilic addition functional groups; and heterocyclic structures such as N, P, S, B, etc., which are prone to nucleophilic and electrophilic reactions Organics II, such as imidazole, cinchonine, methylimidazole, dimethylimidazole, imidazolyl amino acids, histidine, etc.; and polyhydroxy functional group organics III, such as ascorbic acid, glucose, xylitol, fructose, chitosan, phenol , resorcinol, etc., which are prone to elimination reaction, organic replacement, substitution reaction, and the formation of organic substances such as hydrogen bonds. The ratio of organic matter I, II, and III ranges from 1 to 4:1 to 4:1, accounting for 80 to 97% of the total organic matter added.

The precious metal dilute solution is one or more of the acids, bases, salts, etc. of precious and precious metal elements such as Pt, Pd, Ir, Ru, Rh, Au, and Ag; for example, the Pt precursor includes H ₂ PtCl _6. K ₂ PtCl ₄ , ammonium chloroplatinate, platinum acetylacetonate, Pt(NH ₃ ) ₆ Cl ₂ , Pt(NH ₃ ) ₄ Cl ₂ , Pt(NO ₂ ) ₂ (NH ₃ ) ₂ ; the Ir precursor The precursors include chloroiridic acid, iridium chloride, etc.; the Pd precursors include chloropalladic acid, potassium chloropalladate, palladium chloride, and the like. The solvent used includes one or a mixed solution of H ₂ O, CH ₃ CH ₂ OH, ethylene glycol, propanol, and isopropanol. The solution concentration is 0.005～0.15mol/L.

The described pH adjustment range is 6 to 9, and the pH adjustment agent includes urea, potassium citrate, ammonium carbonate, potassium carbonate, sodium carbonate, sodium bicarbonate, sodium thiosulfate, ammonium bicarbonate, diethylenetriamine , aniline, triethylenetetramine, ethylenediamine, 1,10-o-phenanthroline or 2,2'-bipyridine in one or more mixtures. The pore-forming agent gradually decomposes and dissipates in the process of pyrolysis and reduction. It is mainly composed of easily decomposed salts and organic substances, including ZnCl ₂ , SnCl ₄ , FeCl ₃ , nickel chloride and other low-boiling point metal salts and ammonium chloride and ammonium hypochlorite. , oxalic acid, ammonium bicarbonate, ammonium carbonate, ammonium citrate and other high-temperature decomposition organics, and the pore-forming agent accounts for 20-45% of the total amount of the added material.

The processing atmosphere when the precursor powder is further integrated with pyrolysis reduction and carbonization is: methane, hydrogen, nitrogen, H ₂ /He, H ₂ /CO, H ₂ /CO ₂ , H ₂ /N ₂ , H ₂ One or more of neutral or reducing gases such as /Ar, ammonia, NH ₃ /N ₂ , NH ₃ /Ar, carbon monoxide, etc.; the heating rate is 1℃/min～15℃/min; the protective gas flow rate is 80 ~400sccm/min, thereby obtaining atomically dispersed high-activity noble metal catalysts.

Elemental analysis of the catalyst surface: 82-91% of carbon atoms (atomic), 1.5-5% of N (atomic); 2-6% of O element elements; 0.3-4% of surface Pt (atomic), Zn2p It accounts for 0.5-6% (atomic); the total loading of bulk precious metals is 1-20%, and the metal particle size is 2-4 nm; the catalyst structure is mainly spherical. The amount of catalyst Pt is low, and the oxygen reduction activity is comparable to that of commercial Pt/C catalysts, which is of great significance for reducing catalyst costs and reducing the use of precious metals such as Pt.

The invention adopts the method of pyrolysis reduction to prepare the electrochemical catalyst with atomic-level dispersion of noble metal in batches, which can significantly improve the utilization rate of noble metal, reduce the cost of catalysis, and improve the stability of catalyst activity at the same time. The catalyst preparation method is simple, the raw material sources are wide and readily available, and the catalyst can be prepared on a large scale. By increasing the dispersion of precious metals, the utilization rate of precious metals is improved, and the catalytic performance is improved.

Example

The present invention is described in more detail by way of examples, but the present invention is not limited to the following examples.

Example 1

Dissolve 0.5 g of sodium dodecylbenzenesulfonate in 60 mL of deionized water, stir well, and heat to 110°C. 1.5g of tannic acid, 1.5g of imidazole and 0.5g of ascorbic acid were respectively dissolved in deionized water and added to the reaction vessel in sequence, and stirred and heated at 110°C for 2h to prepare macrocyclic organic framework materials. 50 mL of 0.016 mol/L chloroplatinic acid solution was added, and stirring was continued at 110° C. for 2 h. 1 g of urea was added to adjust the pH of the solution, the pH of the solution was 6-7, and stirring was continued at 110 °C for 2 h; 1.5 g of pore-forming agent ZnCl ₂ was added, and the solution was stirred at 110 °C overnight. The obtained precursor solution was poured into an autoclave for hydrothermal crystallization, the reaction temperature was 110 °C, the reaction time was 24 h, the precursor precipitate was obtained by centrifugation, and dried at 80 °C. The precursor powder was pyrolyzed, carbonized and reduced in a hydrogen-nitrogen mixed gas atmosphere, the reaction temperature was 950 °C, the reaction time was 2 h, and the heating rate was 5 °C/min. After cooling, it was replaced with nitrogen, removed, and ground to obtain an integrated atomically dispersed Pt catalyst, which was marked as MOF-Pt(H ₂ )-II. When 25 mL of chloroplatinic acid was added, the sample was labeled as MOF-Pt(H ₂ )-I, and when 75 mL of chloroplatinic acid was added, the prepared sample was labeled as MOF-Pt(H ₂ )-III.

Example 2

Dissolve 0.5 g of sodium dodecylbenzenesulfonate in 60 mL of deionized water, stir well, and heat to 110°C. 1.5g of tannic acid, 1.5g of imidazole and 0.5g of ascorbic acid were respectively dissolved in deionized water and added to the reaction vessel in sequence, and stirred and heated at 110°C for 2h to prepare macrocyclic organic framework materials. 50 mL of 0.016 mol/L chloroplatinic acid solution was added, and stirring was continued at 110° C. for 2 h. 1 g of urea was added to adjust the pH of the solution, the pH of the solution was 6-7, and stirring was continued at 110 °C for 2 h; 1.5 g of pore-forming agent ZnCl ₂ was added, and the solution was stirred at 110 °C overnight. The obtained precursor solution was poured into an autoclave for hydrothermal crystallization, the reaction temperature was 110 °C, the reaction time was 24 h, the precursor precipitate was obtained by centrifugation, and dried at 80 °C. The precursor powder was pyrolyzed, carbonized and reduced in a nitrogen atmosphere, the reaction temperature was 950 °C, the reaction time was 2 h, and the heating rate was 5 °C/min. After cooling, it was replaced with nitrogen, removed, and ground to obtain an integrated atomically dispersed Pt catalyst, which was marked as MOF-Pt(N ₂ )-II. When 25 mL of chloroplatinic acid was added, the sample was labeled as MOF-Pt(N ₂ )-I, and when 75 mL of chloroplatinic acid was added, the prepared sample was labeled as MOF-Pt(N ₂ )-III.

Example 3

Dissolve 0.5 g of sodium dodecylbenzenesulfonate in 60 mL of deionized water, stir well, and heat to 110°C. 1.5g of tannic acid, 1.5g of imidazole and 0.5g of ascorbic acid were respectively dissolved in deionized water and added to the reaction vessel in sequence, and stirred and heated at 110°C for 2h to prepare macrocyclic organic framework materials. 25 mL of 0.016 mol/L chloroplatinic acid solution was added, and stirring was continued at 110° C. for 2 h. 1 g of urea was added to adjust the pH of the solution, the pH of the solution was 6-7, and stirring was continued at 110 °C for 2 h; 1.5 g of pore-forming agent ZnCl ₂ was added, and the solution was stirred at 110 °C overnight. The obtained precursor solution was poured into an autoclave for hydrothermal crystallization, the reaction temperature was 110 °C, the reaction time was 24 h, the precursor precipitate was obtained by centrifugation, and dried at 80 °C. The precursor powder was pyrolyzed, carbonized and reduced in a mixed gas atmosphere of hydrogen and nitrogen. The reaction temperature was 800 °C, the reaction time was 2 h, and the heating rate was 5 °C/min. After cooling, it was replaced with nitrogen, removed, and ground to obtain an integrated atomically dispersed Pt catalyst, which was marked as MOF-Pt(H ₂ )-800.

Example 4

Electrochemical tests were performed in a three-electrode system to characterize the oxygen reduction activity and electrochemical stability of the catalysts. The electrolyte solution of the three-electrode system is 0.1mol L ^-1 of HClO ₄ , the counter electrode is a graphite rod electrode, the reference electrode is a saturated calomel electrode, the cyclic voltammetry test electrolyte solution is saturated with N ₂ , the test system is Gamry3000; ORR test solution Saturated with _O2 , accelerated aging tests were performed in _O2 -saturated 0.1 M perchloric acid. Preparation of catalytic layer of rotating disk electrode membrane: 40% commercial Pt/C catalyst: 5 mg catalyst, 2.5 mL isopropanol, ultrasonic; add 25 μL of 5wt% Nafion solution, ultrasonic, take 3.2 μL of the above dispersed slurry and coat On the surface of the rotating disk electrode, it is used as the working electrode. Due to the low loading of MOF-Pt catalyst, the membrane catalytic layer was prepared: 5 mg catalyst, dispersed by ultrasonic; 25 μL of 5wt% Nafion solution was added, ultrasonic, and 10 μL of the above dispersed slurry was coated on the surface of the rotating disk electrode as the working electrode. Cyclic voltammetry test: 0.1M HClO ₄ , N ₂ saturation, 0.05～1.2VRHE, 50mV/s. ORR test: 0.1M HClO ₄ , O ₂ saturation, 0.2～1.0VRHE, 10mV/s, 1600rpm. Accelerated aging test: 0.1M HClO ₄ , O ₂ saturation, 0.6～1.2VRHE, 100mV/s.

Figure 1 is a TEM image of the catalyst No. II prepared in Example 1. The low-power electron microscope images (a) and (b) show that under the action of atomic-level hyperdispersion of the noble metal in the precursor, after high temperature pyrolysis reduction, the metal is on the surface of the catalyst. Still evenly distributed. Under high magnification (c), the catalyst size is 2-4 nm.

Fig. 2 is the XRD pattern of No. II catalyst prepared in Example 1. The preparation method is conducive to the enrichment and dispersion of Pt on the catalyst surface and improves the utilization rate of Pt. The phase analysis of the catalyst surface is consistent with the standard card JCPDS:00-006- The 0604 card is consistent, the catalyst composition is a single PtZn alloy, and its peak positions are (001), 25.354°, (110), 31.183°, (111), 40.798°, (200) 44.833°, (002) 52.23°, (112) ), 62.213°, (220), 65.495°, (202), 71.34°, (310), 74.336°, (311), 80.11°, (222), 88.390° to match.

3 is an XPS elemental analysis diagram of the catalyst prepared in Example 1. (a) XPS diagram of N1s, N accounted for 3.8% (atomic), and the higher N doping ratio increases the catalytic active sites. (b) XPS image of Pt4f with 1.17% Pt on the surface (atomic), (c) XPS image of O1s with 4.54% O (atomic), (d) XPS image of Zn2p with 1.38% Zn2p (atomic), catalyst The surface elements are evenly distributed.

Fig. 4 is the electrochemical performance characterization diagram of the catalyst prepared in Example 2 of the present invention. (a) The ORR activity of the catalysts prepared by carbonization reduction in N gas atmosphere is not very different despite the different proportions of precursors added _; but the catalysts have significant oxygen reduction activity and a large electrochemical active area; (b) the oxygen reduction peak potential is obvious, have better ORR activity.

FIG. 5 is a graph showing the electrochemical performance of the catalyst prepared in Example 1 of the present invention. (a) The alloy catalyst has good oxygen reduction activity; (b) the oxygen reduction peak potential is significantly higher, and it has better ORR activity.

FIG. 6 is a graph showing the electrochemical performance of the catalyst prepared in Example 1 of the present invention. (a) The alloy catalyst has good oxygen reduction activity, and the catalyst has a high specific surface area, and the electrochemical active area is significantly higher than that of the commercial catalyst; (b) The oxygen reduction peak potential is significantly higher than that of the commercial catalyst, and has better ORR activity.

7 is a graph showing the electrochemical performance of the catalyst prepared in Example 3 of the present invention. Compared with the performance of catalysts prepared under different atmospheres, reducing atmospheres such as hydrogen are relatively more advantageous.

Industrial Applicability

The catalyst preparation technology of the invention is suitable for electrochemical catalysis fields such as fuel cells, water electrolysis, sulfur dioxide oxidation, carbon dioxide reduction, alcohol oxidation, etc., and can prepare ultra-dispersed precious metal catalysts in batches, with good catalyst activity and stability. Chemical catalytic processes have important value and applications.

This embodiment is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention. , all should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (10)

1. A preparation method of an electrochemical catalyst capable of realizing mass amplification and noble metal atomic-level dispersion is characterized by comprising the following steps:

1) preparing an organic framework structure material;

2) chelating an organic framework structure material with noble metal ions;

3) preparing a precursor mixture solution of a noble metal macrocyclic organic substance containing a decomposition type pore-forming agent;

4) carrying out hydrothermal crystallization treatment on the noble metal macrocyclic organic precursor mixture solution to obtain noble metal macrocyclic organic precursor powder;

5) and (3) integrating the further pyrolysis reduction and carbonization of the precursor powder of the noble metal macrocyclic organic matter.

2. The method of claim 1, wherein in step 1), under the action of the surfactant, the macrocyclic organic molecule combines and reacts to form a stable organic framework material.

3. The method according to claim 2, wherein in step 1), the temperature range of the combination and reaction of the macrocyclic organic molecules is 90-140 ℃, and the reaction time is 0.5-3.5 h;

the surfactant in the step 1) is an ionic surfactant, and accounts for 3-15% of the feeding ratio of organic substances;

step 1) the macrocyclic organic molecules used for forming the organic framework comprise three types, namely a macrocyclic organic compound I with nucleophilic and electrophilic addition functional groups; the macrocyclic organic matter II has a heterocyclic structure and is easy to generate nucleophilic and electrophilic reactions; thirdly, a polyhydroxy functional group macrocyclic organic compound III, wherein the proportion of the macrocyclic organic compounds I, II and III is 1-4: 1-4: 1, accounting for 80-97% of the total organic matter addition; the addition amount of the alkali is 0-5%.

4. The method of claim 1, wherein in step 2), the macrocyclic organic framework material and the noble metal ion are substantially chelated by adding a dilute solution comprising the noble metal ion to the solution comprising the organic framework material.

5. The method according to claim 4, wherein the noble metal chelating reaction temperature in step 2) is 90-140 ℃, and the reaction time is 0.5-3.5 h;

the noble metal dilute solution in the step 2) is one or more of acid, alkali and salt of noble metal elements such as Pt, Pd, Ir, Ru, Rh, Au and Ag; using a solvent comprising H₂O、CH₃CH₂One or more of OH, ethylene glycol, propanol and isopropanol; the concentration of the solution is 0.005-0.15 mol/L.

6. The method according to claim 1, wherein in the step 3), a slow-release pH regulator is added to regulate the pH value of the system; adding a pore-forming agent, and uniformly dispersing in the system; and performing coprecipitation on the precursors to obtain a precursor mixture of the noble metal macrocyclic organic compound.

7. The method according to claim 6, wherein the reaction time after the pH adjustment in the step 3) is 0.5-3.5 h, and the reaction temperature is 90-140 ℃; after the decomposition type pore-forming agent is added, fully homogenizing, and reacting at the temperature of 90-140 ℃ for 0.5-3.5 h under the stirring action;

step 3) adjusting the pH value to be 6-9, wherein the pH regulator comprises one or a mixture of more of urea, potassium citrate, ammonium carbonate, potassium carbonate, sodium bicarbonate, sodium thiosulfate, ammonium bicarbonate, diethylenetriamine, aniline, triethylenetetramine, ethylenediamine, 1, 10-phenanthroline or 2, 2' -bipyridyl;

the decomposition type pore-forming agent is easily decomposed salt and organic matters, the pore-forming agent accounts for 20-45% of the total amount of the added substances, and the added substances comprise all added components except the solvent.

8. The method as claimed in claim 1, wherein in the hydrothermal crystallization treatment in the step 4), the precursor growth and aging reaction temperature is 90-140 ℃, and the reaction time is 10-48 h; in the step 4), after hydrothermal crystallization treatment, drying treatment is carried out, wherein the drying treatment temperature is 60-100 ℃, and the drying treatment time is 6-16 h; the temperature of the further pyrolysis reduction and carbonization integrated treatment in the step 5) is 600-1000 ℃, and the time is 0.5-4 h; in the step 5), the precursor powder is further pyrolyzed, reduced and carbonized into an integrated atmosphere, and the treated atmosphere is one or more of neutral or reducing gases; the temperature rising speed is 1-15 ℃/min; the flow rate of the protective gas is 80-400 sccm/min.

9. A catalyst made according to the method of any one of claims 1-8.

10. A mass scalable noble metal atomic-scale dispersed electrochemical catalyst, wherein the catalyst surface elemental analysis: 82-91% (atomic) of carbon atom percent, and 1.5-5% (atomic) of N; the atomic percentage of the O element is 2-6%; 0.3-4% (atomic) of Pt on the surface and 0.5-6% (atomic) of Zn2 p; the total loading of bulk precious metals is 1-20%, and the particle size of the metals is 2-4 nm; the catalyst structure is mainly spherical.

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